The present invention relates to a compound packing container and, more specifically to a double container in which an inner bag member made of a waterproof sheet material is contained in an outer container made of a paper material such as paper, paperboard, or corrugated cardboard.
Previously, various proposals on improvements in construction of this kind of packing container have been made and put into practical usse. However, a typical container of the prior art constructed by forming waterproof sheet material into a tubular member. The tubular member is then inserted into an outer tubular casing. Thereafter, the inner tubular member is tightly sealed at its lower edge and is charged with the material to be packaged. The inner member is then tightly sealed at its upper edge. In addition, it is further required that the outer tubular casing be closed at its lower and upper ends. Thus, the manufacturing and packing process is complicated and time consuming.
To eliminate this problem, there has been recently proposed a container constructed by forming a waterproof sheet material into a self-opening square bag member of gusseted type. The bag member is inserted in an outer tubular casing, as disclosed, for instance, in Japanese Utility Model Publication No. 39297/Showa 50 (1975). However, this type of double container is defective in that manufacturing of the self-opening gusseted type bag member is burdened with difficulties and consequently is liable to insufficient sealing at the gusseted portions.